Summary Aging is a gradual process that results in the loss of cellular function across the body, leading to numerous chronic diseases that promote mortality. Elucidating the precise mechanisms of aging is critical for reducing illness and extending healthy lifespan. However, almost every tissue in the body is modified by aging, making it difficult to pinpoint the principal controller of aging. The goal of this proposal is to determine whether the brain modulates aging through coordinated activity patterns within discrete neuronal networks. We will use one of the shortest-living vertebrates, the African turquoise killifish, as a rapid, high-throughput model of aging to uncover genetically- defined neurons that regulate cellular metabolism and lifespan. Employing large-scale light-sheet imaging in killifish, we will visualize brain-wide calcium activity dynamics to unbiasedly identify neurons that respond to longevity interventions. We will characterize the genetic profiles of the identified neurons via a combination of immunohistochemical, single cell, and phosphorylated ribosome capture approaches. To examine whether these neurons play a causal role to control overall cellular function in the brain and other tissues, we will optogenetically activate these neurons and measure molecular signatures of youth and in vivo metabolic activity in the brain and peripheral tissues. We will monitor and manipulate neural activity throughout the short lifespan of killifish using fiber photometry to determine if this ?neural pacemaker? dictates the tempo of aging and youthful behavior. These approaches will then be extended to longer-lived species ? zebrafish and mice. Knowledge resulting from these studies should be transformative to understand the fundamental mechanisms that regulate and synchronize aging and longevity. As age is the prime risk factor for many diseases, including neurodegenerative diseases, this proposal should provide new, circuit-based approaches to treat these diseases. !